import math

x_1,y_1,x_2,y_2 =map(float,raw_input().split())
print (math.sqrt(math.pow(x_2-x_1,2)+math.pow(y_2-y_1,2))) import math math x_1,y_1,x_2,y_2 =map(float,raw_input().split()) x_1 map(float,raw_input().split()) map float raw_input().split() ().split () raw_input split y_1 x_2 y_2 print (math.sqrt(math.pow(x_2-x_1,2)+math.pow(y_2-y_1,2))) print math.sqrt(math.pow(x_2-x_1,2)+math.pow(y_2-y_1,2)) math.sqrt math sqrt math.pow(x_2-x_1,2)+math.pow(y_2-y_1,2) math.pow(x_2-x_1,2) math.pow math pow x_2-x_1 x_2 x_1 2 math.pow(y_2-y_1,2) math.pow math pow y_2-y_1 y_2 y_1 2 y_2 =map(float,raw_input().split()) map(float,raw_input().split()) y_2 y_1,x_2,y_2 =map(float,raw_input().split()) map(float,raw_input().split()) y_1 x_2,y_2 =map(float,raw_input().split()) map(float,raw_input().split()) x_2 x_1,y_1,x_2,y_2 =map(float,raw_input().split()) map(float,raw_input().split()) x_1
import math

x_1,y_1,x_2,y_2 =map(float,raw_input().split())
print (math.sqrt(math.pow(x_2-x_1,2)+math.pow(y_2-y_1,2)))